The reason why a lot of people have trouble getting back with their ex after a break up is because they go about everything the wrong way...
First they try to beg and plead for forgiveness or try to argue with their ex to get back together...
Then they'll try calling their ex a bunch of times (it's worst when they're under the influence) and all it will do is annoy the other person and push them away for good.
You have to take the opposite approach; instead of breaking down and being an emotional wreck you have to be strong, and independent with a positive outlook.
If your boyfriend or girlfriend wants to call it quits just go right along with it, go with the flow don't push back against it; it will be a losing battle every time.
Instead of calling all of the time, try writing a simple hand written note which just agrees with the break up and tells them you agree with them and think its for the best.
It sounds crazy but this stuff does work.
You need to let go of any insecurities, control issues, or general bad habits that initially brought on the break up.
Make yourself busy to keep your mind off of the break up for the first couple weeks, you can't contact your ex right away, you have to come off as if you were really fine with the break up and you are already moving on without a second thought.